B.1(22) says that an Import pragma must be the completion of a
declaration, and 6.1(20) says that a completion is not allowed for an
abstract subprogram declaration.

With the following patch, the attached example gives

  5.    pragma Import (Ada, p1);
                            |
     >>> cannot import abstract subprogram "p1" declared at line 4

whereas without it the no error is reported and the compilation is
succesful.

Bootstrapped and regtested on x86_64-linux. Ok for trunk?

    gcc/ada/
	PR ada/38333
	* sem_prag.adb (Process_Import_Or_Interface): Forbid an abstract
	subprogram to be completed with a "pragma Import".

    gcc/testsuite/
	PR ada/38333
	* gnat.dg/specs/import_abstract.ads: New.
---
 gcc/ada/sem_prag.adb                            |    9 +++++++++
 gcc/testsuite/gnat.dg/specs/import_abstract.ads |    6 ++++++
 2 files changed, 15 insertions(+), 0 deletions(-)
 create mode 100644 gcc/testsuite/gnat.dg/specs/import_abstract.ads

diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
index 065cb97..4e43b66 100644
--- a/src/gcc/ada/sem_prag.adb
+++ b/src/gcc/ada/sem_prag.adb
@@ -3455,6 +3455,15 @@ package body Sem_Prag is
                else
                   Set_Imported (Def_Id);
 
+                  if Is_Subprogram (Def_Id)
+                    and then Is_Abstract_Subprogram (Def_Id)
+                  then
+                     Error_Msg_Sloc := Sloc (Def_Id);
+                     Error_Msg_NE
+                       ("cannot import abstract subprogram& declared#",
+                        Arg2, Def_Id);
+                  end if;
+
                   --  Special processing for Convention_Intrinsic
 
                   if C = Convention_Intrinsic then
diff --git a/gcc/testsuite/gnat.dg/specs/import_abstract.ads b/gcc/testsuite/gnat.dg/specs/import_abstract.ads
new file mode 100644
index 0000000..9d05f0c
--- /dev/null
+++ b/src/gcc/testsuite/gnat.dg/specs/import_abstract.ads
@@ -0,0 +1,6 @@
+-- { dg-do compile }
+package Import_Abstract is
+   type T1 is abstract tagged null record;
+   procedure p1(X : T1) is abstract;
+   pragma Import (Ada, p1);    -- { dg-error "cannot import abstract subprogram" }
+end Import_Abstract;
-- 
1.6.0.4.880.g80093
